In vehicle collisions a chief cause of injury is the extreme impulses experienced; the human body has a limited ability to cope with accelerations experienced over given durations of time. For example, the US Federal Motor Vehicle Safety Standards specify maximum allowable measures listed in FIGS. 1a and 1b. 
To lower the maximum impulse experienced, the distance through which the body travels when changing its initial to final velocity must be increased, or equivalently, the time during which the acceleration is experienced must be increased. For example, in a head-on collision of a vehicle with a rigid wall, the occupant's body will undergo a change from the vehicle's initial speed to zero speed within a certain distance. The acceleration undergone is determined by the initial velocity and this distance. If this distance can be increased, the acceleration will be decreased. Care must be taken that the passengers will experience the maximum possible acceptable impulse or less, which can be accomplished by use of energy-absorbing elements of suitable design, devices to increase the travel available to the occupant, or both. The ideal energy absorber connecting a passenger to the rest of a vehicle transmits the maximum acceptable stress to the occupant or less, reaching this level after a minimum of travel. It would transmit this level of stress and no more, no matter the level of stress imparted to it.
Solutions known from the prior art provide shock absorbing seats based on different types of elastic or plastic deformation or breakage of metallic components, collapsible bar mounts or columns made of metals and/or composite materials, crushable honeycomb, etc. Some available solutions present a full system including both an original seat and a built-in integrated absorbing mechanism.
U.S. Pat. No. 5,685,603 discloses an apparatus for a vehicle includes a child seat for holding a child. A support device supports the child seat on a seat of the vehicle for movement relative to the seat during a collision in which at least one condition exceeds a predetermined threshold. An energy absorbing device absorbs kinetic energy of the child and the child seat during such relative movement. The support device may include support bars that permit sliding movement of the child seat relative to the support bars and the vehicle seat. Several types of energy absorbing devices may be used, including compressible bellows, cut able strips of sacrificial material, crushable pieces of sacrificial material, deformable projections, a payout device with webbing, compressible shock absorber assemblies, and slid able frictionally engaging portions.
U.S. Pat. No. 5,152,578 a front leg is formed by an upright support rod extending vertically above a fixing stud, a rear leg is formed by both a lower support rod extending on a diagonal line joining the upper end of the front leg and the lower end of the rear leg and an upper support rod contiguous to the lower support rod in an upper position relative to the lower support rod, the upper support rod being curved accurately and inclined rearward and upwards, and an energy absorber is mounted bridge wise as a diagonal member between the upper end portion of the front leg and the lower end portion of the rear leg, to constitute a leg structure. Accordingly to this leg structure, a striking energy is absorbed by an anti-plastic deformation force induced when the rear leg and the energy absorber is deformed plastically under an impact larger than a predetermined value, and the seat is held at its supported posture in normal use. This leg structure can be utilized not only in aircraft but also in automobiles and railway vehicles.
A major difference between the current invention and the prior art is the ability to determine the exact position of the system under any give load and direction of the load. In the prior art, different impacts will apply different forces on the energy absorbing components. Greater load applied on the rear leg, will change the orientation of the seat differently than forces applied mainly on the front leg.
The change in orientation will affect the forces transferred to the occupant from the energy absorbing components (legs and cylinder).
Thus, if a simple, analytical and repeatable system is desired with optimized energy absorption mechanism, it is better to use a system with only one deforming component (i.e. spiral).
Designing a system with specific force-deflection curve which transfers predetermined forces to the occupant requires careful design of the mechanism and the use of a highly controllable EA element such as the spiral.
US Patent application 20030209926 discloses a child seat device formed of a base to be placed on a seat of a car, a child seat body placed on the base, and a connecting member for connecting a rear bottom of the child seat body to a fixed portion. The connecting member increases a length thereof while absorbing a kinetic energy of the child seat body when a tension higher than a predetermined value is applied thereto from the child seat body.
Hence there is a long felt and unmet need to provide a simple and cheap vehicle passenger safety seat which absorbs energy in tension and compression suitable for mass production.